Fluidic volume-cycled respirator

ABSTRACT

A fluidic, volume-cycled respirator circuit comprising a fluidic flowmeter, a tidal volume selection controller and an inlet valve. The flowmeter is connected to the controller through a transmitting means which transmits gas flow frequency signals. Said controller is then connected to the inlet valve, which is connected back to the flowmeter; hence, the respirator circuit is complete. The tidal volume selection controller may operate by either fluidics, electronics, or the combination of the two. The flowmeter facilitates supply of air to the patient. The amount of air supplied is controlled by the tidal volume selection controller which senses inspiration and gas flow frequency. The controller is equipped with a timer back-up system in the event that either the system or the patient fail to respond. The valve is operated at the direction of the tidal volume selection controller. The valve is open during the inspiratory phase and closed during the exhalation phase. The respirator herein overcomes the use of burdensome piston-bellows assemblies, has few moving parts and is relatively small in size. The use of piston-bellows assemblies is avoided by the use of a fluidic oscillator flowmeter.

RIGHTS OF THE GOVERNMENT

The invention described herein may be manufactured, used and licensed byor for the U.S. Government without payment to us of any royalty thereon.

BACKGROUND OF THE INVENTION

Volume-cycled respirators which have been used in the past and thosewhich are presently in use are cumbersome in nature. Most of them makeuse of piston-bellows assemblies to deliver the tidal volumes ofbreathing gas to the patient. Conventional respirators are fairlycomplex and further employ a variety of elements including snap valves,springs, solenoid valves, magnets, gear boxes, ratchets, mechanicallinkages, pulleys, photocells, electronic circuitry, and othercomponents to provide a number of functions. The complexity and hybridnature of these systems results in large, massive and expensiverespirator units which are somewhat fragile and susceptible tomechanical failure. Basically, most of them have numerous moving partswhich makes the apparatus more complex to operate and maintain.

The present invention relates to a fluidic volume-cycled respiratorcircuit which is relatively simple in its construction; contains few, ifany, moving parts; is highly efficient; and is convenient to use andtransport. The respirator herein basically comprises an input valve, aflowmeter and a controller.

In order to better understand the present invention, one shouldunderstand the prior art teachings in the field of respirators.

Respirators comprising (1) a control circuit which is responsive to a(2) sensor are taught by Durkan and Durkan et al. in U.S. Pat. Nos.4,462,398; 4,506,666; 4,519,387 and 4,570,631. The control circuitsdescribed therein operate an input valve. The sensor picks up thenegative pressure sensed from the patient using the respirator. Thesensor then, in accordance with its sensing of the negative pressure,instructs the control circuit to operate the input valve in response tothe patients' needs. The control circuit may also operate the valve ifno negative pressure is sensed within a predetermined time period.Hence, the respirator disclosed operates based on the change in pressurefrom the patient and based on a predetermined time set to control thesupply valve. Note that the patents may additionally make use of aconventional flowmeter. The sensor taught may be fluidic; and the valveis electrically controlled by the control circuit. The patents furtherteach generally that other fluidic elements can be used in theirrespirator circuit.

The Durkan and Durkan et al. references discussed above are veryelaborate breathing devices. They make use of both fluidics andelectronics in their sensor means and control circuits. The fluidicdevices are fluidic amplifiers. Based on the description of the Durkanpatients above it may appear that these references teach our invention.This is not so because our invention is able to provide the same serviceas Durkan but using a more reliable and compact system. The respiratorherein is not as complex as those taught by these patent references.Moreover, our invention makes use of fluidic oscillators, as opposed tofluidic amplifiers. The use of one is not an obvious sustitution ormodification for the use of the other.

U.S. Pat. No. 4,461,293, issued to Chen, teaches a breathing apparatussimilar to that taught by Durkan. In this teaching, a control circuit isresponsive to a sensor which operates a valve to supply breathing gas toa patient. This system, however, is a more complex system than that ofthe present invention. Moreover, unlike the teaching in Chen, thepresent invention makes use of a fluidic oscillator as the flowmeter asopposed to a fluidic amplifier.

Perkins, U.S. Pat. No. 4,705,034, teaches a respiratory apparatus whichmay use fluidic sensors--note, column 4, lines 49-65. Sensors of thistype are able to detect the onset of inhalation and the volume meteringof the breathing gas. The respirator taught by Perkins is a demandsystem which requires the use of an electrical solenoid to activate theinput valve. In addition, the metering system therein has many movingparts. This system makes use of a piston which our invention avoids.Perkins teaches a much more elaborate system than that of the presentinvention.

U.S. Pat. No. 4,054,133, issued to Myers, teaches a respirator apparatusthat comprises a control means which is responsive to inhalation, pauseand exhalation of a patient. Its response regulates the flow of oxygenfrom a supply chamber to said patient. Reduced pressure activates aninput valve to only allow oxygen flow during inhalation. This breathingapparatus makes use of a diaphragm to sense the pressure differentialdue to the patient's breathing. In addition, nowhere does Myers indicateany use of fluidics in his breathing device.

U.S. Pat. No. 4,381,002, issued to Mon, one of the inventors herein,teaches a respirator which comprises a valve, a fluidic control systemwhich senses inspiration and exhalation, and an oxygen source. Thispatent, however, does not mention the use of a fluidic flowmeter.Moreover, the Mon respirator makes use of a diaphragm and a fluidicamplifier controller, neither of which is within the scope of thepresent invention.

U.S. Pat. No. 4,278,110, issued to Price et al., claims a respiratorwhich utilizes a fluidic valve, a flowmeter, a flow controller whichsenses expiration and inspiration, and an oxygen source. The oxygen issupplied on a demand basis only. A fluidic oscillator is not use inPrice et al. Moreover, our invention does not require the use of afluidic valve.

U.S. Pat. No. 3,896,800 teaches that the use of fluidic and electronicrespirator control devices is well known. The apparatus taught, however,requires the use of a diaphragm.

U.S. Pat. No. 4,019,382, issued to El-Gammal, sets forth the generalteaching of the well-known use of a fluidic flowmeter which measuresrespiratory functions. Note that the flowmeter is for use withcumbersome breathing apparatus. The breathing apparatus does not teachthe respirator circuit claimed herein.

U.S. Pat. Nos. 4,120,300; 4,289,126 and 4,414,982 are recited to givethe reader more background on the general teachings of the use offluidics in the respirator art areas.

The use of fluidics in respirators is not a novel one. Note,"Respiratory Care Applications for Fluidics," Respiratory Therapy, pp.29-32 (1973).

As one may note from the teachings in the prior art with regard torespirators, the individual concepts of using fluidics, control devices,sensors, etc. are not novel. More particularly, the use of fluidiccontrol systems and fluidic sensors are further well known. However, thecombination of these concepts are neither taught nor suggested in theprior respirator art.

It is the combination of these general components which result in thehand-held respirator of the present invention.

BRIEF SUMMARY OF THE INVENTION

This invention deals with a fluidic, volume-cycled respirator circuitcomprising a fluidic oscillator flowmeter, a pressure transducer, atidal volume selection controller and an inlet valve. The flowmeter isconnected through a pressure transducer or microphone to the controller,which is in turn connected to the inlet valve, which is furtherconnected back to the flowmeter. Hence, the respirator circuit iscomplete. The tidal volume selection controller may operate by eitherfluidics, electronics, or a combination of the two. Electronic tidalvolume selection controllers are preferred. The flowmeter facilitatesthe supply of air to the patient. The amount of air supplied iscontrolled by the tidal volume selection controller which senses theinspiration phase, exhalation phase of the patient's breathing, and gasflow frequency passing through the flowmeter. Upon inspiration orexhalation, the valve is operated at the direction of the tidal volumeselection controller to accommodate the needs of the patient. The valveis instructed to open during the inspiratory phase and instructed toclose during the exhalation phase. The valve is additionally closed oncea specific, programmed breathing gas glow frequency has been met. Thiswill be further discussed below.

When the respirator circuit of the present invention is in use, apressurized breathing gas is forced through the inlet valve which isopen during the inspiratory phase of the patient's breathing and isclosed during his exhalation phase. The breathing gas then continuesthrough the inlet valve to a fluidic flowmeter and to the patient inneed. The flowrate of the gas is converted to a frequency signal by theflowmeter. The frequency signal is monitored by a pressure transducer ora microphone which is connected to a controller. Once the controllertranslates the incoming signals to accommodate the needs of the patient,it directs the input valve to either open or close, thus regulating theamount of breathing gas entering the system. The controller is furtherable to detect inspiration of the patient. Inspiration is detected bythe device sensing a change in pressure of the air passing therethroughdue to the patient'S spontaneous breathing. When inspiration of thepatient is detected, the controller instructs the opening of the inputvalve.

The controlling device may, optionally, contain a conventionalelectronic timing circuit which would enable the controller to dictatethe exhalation phase of the breathing cycle to be within preselectedtime limitations. This timing circuit may override the spontaneousresponse or lack of response of the patient.

The fluidic volume-cycled respirator circuit system of the presentinvention requires that the flowmeter therein be fluidic in nature. Thisis critical to the invention. The controlling means, on the other hand,may operate either by fluidics, electronics or a combination of the two.Use of an electronic controlling means is preferred.

Unlike the majority of volume-cycled respiratory devices already on themarket, the volume-cycled respirator of the present invention eliminatesthe use of pistons, bellows and other cumbersome component parts. Therespirator herein is basic in nature and operates efficiently using andcontaining only essential components.

The volume-cycled respirator herein is both reliable and efficient inits operation. It contains few moving parts, if any; and it isessentially maintenance free. Moreover, it is a convenient device to useand carry. Note, that the respirator is relatively small in size--aboutpocket-size.

It is an object of the present invention to provide an efficient andreliable respirator.

It is a further object of the present invention to provide a respiratorwhich is light weight.

It is a further object of the present invention to provide a respiratorwhich is convenient to operate and carry.

It is a further object of the invention to provide a respiratorcontaining few moving parts.

Still a further object of the present invention is to provide arelatively maintenance free respirator.

Other objectives and features of the present invention will be apparentfrom the following detailed description of the invention, drawings andthe claims.

DETAILED DESCRIPTION OF THE INVENTION

The foregoing objectives are achieved by the respirator of the presentinvention. The present invention deals with a respirator made upprimarily of an input valve, a flowmeter and a controller which operatesthe input valve. This respirator is in a circuit configuration.

Any conventional fluidic, oscillator flowmeter may be used in theinvention. The fluidic oscillator creates a closed system in order toaccurately measure the flow of breathing gas passed therethrough.Fluidic flowmeters are true volume flowmeters and contain no movingparts. They assist in controlling the inspiratory phase of the breathingcycle. The flowmeter herein replaces the piston/bellows of the prior artrespirators. This represents the novelty of our invention.

In addition, any conventional tidal volume selection controller tooperate the input valve may be used as the controller. The only criticalrequirements for said controller is that (1) it be able to detectoscillator frequency signals sent by the flowmeter through a microphone;(2) it be able to detect negative pressure signals sent from the patientand through a pressure sensor tube or device; and (3) it be equippedwith a time-cycle time. Based on these requirements, the controller isable to control the input valve according to the method in which it hasbeen programmed by a medical operator. The controller may operate theinlet valve based on a set frequency integration (counter), a set timeperiod or by the spontaneous inspiration of the patient. The controlleris equipped with a totalizer/counter which is set to sense apredetermined number of frequency counts. Conventionaltotalizer/counters such as those manufactured by Redington® Counters,Inc. may be used herein. The counter is one of the programmable featuresof the present invention. The timer may be set to customize therequirements of the individual patient. The controller is programmed toaccommodate the needs of the patient.

More specifically, the fluidic oscillator flowmeter is constructed froma fluidic laminar proportional amplifier having negative feedback. Theflowmeter puts out an output pressure signal which has a frequency thatis a linear function of the volumetric flow rate of breathing gas sentthrough the oscillator flowmeter. This relationship of output pressureand frequency is independent of the type of gas flowing therethrough.The relationship is constant regardless of the gas properties--i.e.density and viscosity. Hence, for the type of fluidic oscillatorflowmeter, the volumetric flow may be represented as

    Q=Kf,                                                      (1)

where

Q=volumetric flow

f=oscillator frequency; and

K=geometric constant

In order to determine the tidal volume (volume of breathing gasdelivered to the patient) of the flowmeter, the flowmeter's volumetricflow output must be integrated over the total time of the inspiratoryphase of the breathing cycle; therefore, ##EQU1## where V=tidal volume;and

T=total time of inspiratory phase

The equation (2) may be simplified and rewritten as ##EQU2## bysubstituting the "Q" with the equivalent "Kf."

The quantity under the integral sign in equation (3) above representsthe oscillator frequency counts over the time period T. Therefore, acertain amount of tidal volume corresponds to a specific oscillatorfrequency count.

The tidal volume selection controller may be either fluidic, electronicor a combination of the two. As discussed above, it senses theoscillator frequency counts and controls the input valve accordingly.For example, if an electronic controller is used, a conventionalmicrophone may be used in the flowmeter to allow the pressureoscillations to be converted into a corresponding electrical signal. Theresulting electrical signal can be processed to accurately perform acounting function. Once a certain count quantity is reached, asprogrammed by an operator, the controller can then send a signal tooperate the input valve that controls the supply of breathing gases.

The controller also contains an electronic timing device which controlsthe breathing cycle in the event that the patient is unable to inhaleand cause a negative pressure to signal the valve to open. Thiselectronic timing circuit maintains the phases within the breathingcycle to stay within a preselected time limit by signaling the inputvalve to either open or close. The preselected time limit is programmedin by the medical operator.

Now that the basic invention has been described, its operation may beunderstood by the following description. When the breathing gas inletvalve is open, gas is forced through a fluidic oscillator flowmeterwhich converts the flow rate to a frequency signal. The frequency isproportional to the volume flow rate. The output flow of gas from theflowmeter is delivered to the patient. The frequency signal is thenmonitored and converted into frequency counts by the use of atransmitting means, such as a microphone. The frequency counts aretransmitted to the tidal volume controller which is equipped with aconventional, electronic frequency counter/totalizer which may beprogrammed. Once the specific oscillator frequency count is reached, thecontroller signals the input valve to close. This ends the inspiratoryphase of the patient's breathing cycle and starts the exhalation phase.The exhalation phase is terminated by an inspiratory effort from thepatient. The inspiratory effort is sensed as a negative pressure by aconventional pressure sensor. This negative pressure is communicated tothe controller in the form of a slight negative pressure signal, onebelow ambient pressure--approximately -0.5 to -4.0 cm of water. Thetidal volume selection controller then instructs the input valve toopen. Hence, a new inspiratory phase is initiated. In the event that thepatient is unable to spontaneously inspire, a timer would kick in inorder to open the input valve. The timer may be programmed toaccommodate the patient. Moreover, the timer may override the othercontroller functions. For instance, if the patient were to resume hisspontaneous inspiration after the timer had kicked in, the timer isconstructed in such a manner which would allow the patient's effort toinhale to override the timer device.

In normal operation, each new respiratory cycle will be initiated eitherwhen the patient attempts to breath (assist mode), or when the presettimer value is reached (control mode), whichever occurs first. Thisopens the input valve. The exhalation portion of the respiratory cycle,which occurs during the period in which the input valve is closed, isinitiated when a preset frequency count is reached (corresponding to aspecific volume of breathing gas), or if the frequency countermalfunctions, when a preset timer value is reached. This closes theinput valve.

Other features of the present invention will be apparent from thefollowing drawings and their description.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a schematic drawing of a fluidic oscillator of the type whichmay be used in the flowmeter set forth in the volume-cycled respiratorof the present invention.

FIG. 2 is a typical oscillator flowmeter circuit comprising a pluralityof the fluidic oscillators of FIG. 1. This oscillator flowmeter circuitmay be used for the flowmeter in our invention.

FIG. 3 is a simplified schematic drawing of the volume-cycled respiratorcircuit of the present invention.

FIG. 4 is a schematic drawing of a tidal volume controller which iswithin the scope of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS AND THE INVENTION

FIG. 1 teaches a schematic representation of a conventional fluidicoscillator 13. Said fluidic oscillator 13 is the type which may be usedin the volume-cycled respirator circuit of the present invention. Theoscillator 13 comprises supply port 12, vent ports 27 and 28, outputports 9, feedback lines 8, and input ports 15. Input ports 15recirculate the fluidic flow resulting from the feedback lines 8. Thisfluidic oscillator 13 measures volume flow rate and is constructed froma fluidic laminar proportional amplifier having negative feedback lines8.

FIG. 2 is a schematic representation of a typical flowmeter circuit 17.In said flowmeter circuit 17, from one to N stages of fluidic laminarproportional amplifiers (LPA) having feedback lines may be used toobtain the required flow rates. Note that the LPAs in FIG. 2 arerepresented as 1, 2 through N. The flowmeter circuit 17 comprises supplyport 23 for the breathing gas, input line 21, feedback line 22,frequency output 25, and exit port 20. Said flowmeter circuit 17, andflowmeter circuits of a similar type, may be used in the volume-cycledrespirator circuit of the present invention.

FIG. 3 represents a simplified schematic figure of the volume-cycledrespirator of the present invention. The volume-cycled respiratorcircuit, generally set forth as 30, comprises breathing gas supply 7which introduces a pressurized breathing gas to the respirator system,control valve 5, conventional pressure regulator 32 fluidic oscillatorflowmeter 10, exit line 6 to patient, transmitting line 4 running fromthe flowmeter 10 through either a pressure transducer or microphone 35to the tidal volume controller 3. Said controller 3 is connected tocontrol valve 5 to complete the volume-cycled respirator circuit 30. Atransmitting line (or tube) 33 running from the patient is connected topressure sensor 34. This allows the pressure sensor 34 to detect thepatient's inspiration effort. Pressure sensor 34 is capable of detectingnegative pressure as low as -0.5 to -4.0 cm of water.

The volume-cycled respirator circuit 30 supplies breathing gas to therespirator system at control valve 5. The breathing gas passes throughinput valve 5 and into fluidic flowmeter 10. The flowmeter 10facilitates the supply of breathing gas to the patient through outputline 6. The patient's breathing response can be transmitted viatransmitting line 33 and registered by pressure sensor 34. Pressuresensor 34 is used to detect even extremely minor changes in pressurecreated by a patient's inspiratory efforts. Once the pressure sensordetects a negative pressure, it communicates said change in pressure tothe tidal volume selection controller 3 which in turn sends an outputsignal which operates input valve 5 to open. The tidal volume selectioncontroller 3 controls the volume of air that enters the volume-cycledrespirator 30 by operating the input valve 5.

The tidal volume controller 3 additionally operates the input valve 5when a set volume of breathing gas has been administered to the patient.The tidal volume controller 3 is equipped with an electroniccounter/totalizer which counts the frequency output of the pressuretransducer or microphone 35. The tidal volume controller 3 may beprogrammed by a medical operator to accommodate the personal needs ofthe patient.

Another avenue in which the tidal volume controller 3 may operate theinput valve 5 is by the use of a timing device incorporated into saidcontroller 3. Said timing device may be programmed in order to regulatethe exhalation phase of the breathing cycle to be within certain timelimits. For example, if for some reason the pressure transducer ormicrophone 35 is malfunctioning (therefore no frequency output isreceived by the controller 3) and the patient has no spontaneousbreathing (therefore no negative pressure signal is sensed by thecontroller 3), the timing device within said controller 3 would takeover and cause the controller 3 to open and close the input valve 5during the set timed intervals.

FIG. 4 illustrates, in some detail, the tidal volume controller 3 whichmay be used in the respirator circuit of the present invention. Thecontroller 3 is equipped with a frequency counter 38, a pressure switch42, a time-cycle timer 45, and a conventional junction 47. Thecontroller 3 is connected in such a manner so as to operate input valve5. The tidal volume controller 3 is positioned to accept frequencysignals from microphone 35 through transmitting line 4. Said signals arecounted by frequency counter 38. Once the set frequency, whichcorresponds to a set volume of breathing gas, is reached, the frequencycounter 38 signals the valve 5 to turn off. The controller 3 also ispositioned to accept signals from pressure sensor 34 throughtransmitting line or tube 33. When the pressure sensor 34 senses anegative pressure caused by the patient's effort to inhale, pressureswitch 42 signals the valve 5 to open and begin another inspiratoryphase. The controller 3 is further equipped with a time-cycle timer 45which is capable of sending a signal to both open and close the valve 5.In the event that the patient is unable to independently inhale andcause a negative pressure to operate the opening of valve 5, thetime-cycle timer 45 will open the valve 5 after a preset time period.Moreover, if frequency counter 38 were to malfunction, said timer 45would override any signals and turn valve 5 off. Hence, timer 45 createsa back-up mode for the respirator of the present invention. Conventionaljunction 47 may be any conventional junction which will serve thepurpose of the present invention, such as a logic circuit junction.

Based on the description set forth, one is able to realize how therespirator within the scope of the invention is extremely reliable andeasily adaptable to the needs of any patient.

The respirator circuit of the present invention can be produced toeasily fit into a relatively small compartment, such as a small boxhaving the measurements of 3 inches by 3 inches by 6 inches. Hence, thisrespirator is much smaller than the conventional volume-cycledrespirators that traditionally make use of bellows or pistons, and areaccompanied by a bulky electric motor.

The respirator circuit herein has numerous advantages over those alreadyon the market. Some of the advantages include lower cost, smaller size,lighter in weight, improved reliability and ease of maintenance.

Although the invention has been described with reference to specificembodiments and drawings, it is to be understood that the invention isnot limited to those precise embodiments, and that various changes andmodifications may be effected by one skilled in the art withoutdeparting from the scope or spirit of the present invention.

We claim:
 1. A fluidic volume-cycled respirator circuit which containsno piston-bellows assembly, said fluidic volume-cycled respiratorcomprisinga breathing gas source; an input valve connected to saidbreathing gas source; a property independent fluidic oscillatorflowmeter which is connected to said input valve and directly to apatient; a means which transmits gas flow frequency signals from theflowmeter to a tidal volume selection controller; a tidal volumeselection controller which is connected to said means and to said inputvalve; and a return transmitting line equipped with a pressure sensorrunning from the patient to said tidal volume selection controller.
 2. Afluidic volume-cycled respirator circuit in accordance with claim 1,wherein said tidal volume selection controller is electronic.
 3. Afluidic volume-cycled respirator circuit in accordance with claim 1,wherein said tidal volume selection controller comprises a frequencycounter, a pressure switch, and a time-cycle timer.
 4. A fluidicvolume-cycled respirator circuit in accordance with claim 1, whereinsaid fluidic oscillator flowmeter is a true volume flowmeter.
 5. Afluidic volume-cycled respirator circuit in accordance with claim 1,wherein said flowmeter has no moving parts.
 6. A method foraccommodating the complete respiratory needs of a patient wherein saidmethod comprisesproviding a breathing gas source connected to abreathing gas inlet valve; opening said gas inlet valve so as to allowbreathing gas to be forced therethrough and subsequently through aproperty independent, fluidic oscillator flowmeter; delivering saidbreathing gas exiting from said fluidic oscillator flowmeter directly tosaid patient; monitoring the flow of said breathing gas by atransmitting means which transmits the oscillator frequency count ofsaid breathing gas to a tidal volume controller; closing said valve oncea preset oscillator frequency count is reached; sensing negativepressure produced by an inspiratory effort from said patient using apressure sensor; communicating said negative pressure to said totalvolume controller which instructs aid breathing gas inlet valve to open;and repeating the breathing cycle;wherein said flowmeter converts thebreathing gas flow rate to a frequency signal which is converted intosaid frequency counts by the use of said transmitting means; and whereinsaid tidal volume controller operates said breathing gas inlet valvecausing said valve to close once said preset oscillator frequency countis reached.